Lighted ceiling fixtures for buses, coaches, subway cars, transit vehicles and the like have come into use which provide the dual function of interior illumination as well as back lighting a translucent advertising card. Such units are shown for example, in the U.S. Pat. Nos., of Jayne, 2,336,016 of 1943 and Schwenkler, 3,210,875 and 3,211,904, both of 1965, and are commonly provided with a light-transmitting cover which has inwardly turned flanges within which relatively stiff printed advertising cards are received for back lighting.
The advertising cards which have commonly been used with back-lighted fixtures are normally transparencies which are silk-screened on both sides of du Pont Mylar sheets or similar relatively heavy transparent plastic material of 0.010 inch thickness or greater. Such relatively heavy material is required so that the cards are self-retaining when supported only at the edges, and silk screening is commonly required on both the front and the back surfaces to prevent pin holes. Such advertising cards are commonly 11 .times. 21 inches or 11 .times. 28 inches in size and may cost about $1.85 each in four colors in large quantities of about one thousand. When they are back lighted they provide an attractive and eye-catching advertising display.
It has long been recognized that advertising copy can more economically be printed on ordinary board-type paper in local printing shops. However, when such material is printed on cardboard, it does not transmit any light when back lighted and when such advertising material is used in back-lighted fixtures, as it often is, there is obviously no back-lighted effect. However, cardboard type cards are often used in front lighted fixtures of the type shown, for example, in the U.S. Pat. No. of Arenberg, 2,587,807 of 1952.